Mental traits and neurological diseases will be studied and analyzed with a view to determing the components in their etiology, and where possible the mode of genetic action determined. Schizophrenia, autism, affective disorders and ataxia as well as other mental diseases and causes of mental retardation will be studied in large pedigrees, and any genes found to cause these diseases will be mapped on the human genome by family linkage analyses. New statistical techniques will be devised for this purpose, allowing for both qualitative and quantitative multifactorial traits, single- and multiple-generation data. Appropriate computer programs will be written, and applied both to data that have already been collected and to data that will be collected with the special purpose of identifying major genes for such traits. The possible existence of such major genes will be demonstrated by segregation analysis and by searching for linkage relationships between such genes and polymorphic marker genes in blood. The statisitical methods will be tested for power and robustness by simulation methods. This research will lead to a more complete understanding of the determinants involved in the mental diseases studied, to more accurate genetic counselling, and hence to increased possibilities for prevention and/or early treatment.